Progressing cavity pump/motor

ABSTRACT

A progressing cavity pump/motor includes a stator ( 12 ) having a metal interior surface ( 14 ) and one or more spiraling internal lobes ( 16 ). The rotor ( 18 ) has a metal exterior surface ( 20 ) and one or more spiraling external lobes ( 22 ) for cooperating with the stator to form progressing cavities between the stator and the rotor during rotation of the rotor. At least one of the stator interior surface and the rotor exterior surface include a plurality of spaced grooves ( 30 ) in the respective surface, such that fluid flowing to a gap between the stator and the rotor is disrupted by the spaced grooves to reduce fluid leakage between the stator and the rotor.

STATEMENT OF RELATED APPLICATION

This application is a continuation application depending from andclaiming priority to application Ser. No. 13/082,210 filed on Apr. 7,2011 and having the same title.

FIELD OF THE INVENTION

The present invention relates to a progressing cavity pump/motor, andmore particularly to a progressing cavity pump/motor suitable for hightemperature applications wherein both the interior surface of the statorand the exterior surface of the rotor are formed from a substantiallyrigid material.

BACKGROUND OF THE INVENTION

Progressing cavity pumps are used in various applications, includingdownhole oilfield applications to pump fluids to the surface.Progressing cavity downhole motors are similar tools commonly used toconvert hydraulic energy into mechanical energy, e.g., to rotate a drillbit. The interior surface of the stator is typically formed from anelastomeric material which acts as a contact seal with the rotor. Thecontact areas determine the perimeter of the cavities which contain theworking fluid, and these cavities progress from one end of thepump/motor to the other end of the pump/motor during its operation.

In certain applications, the operational temperature range intended forthe pump/motor exceeds the practical maximum temperature of elastomericmaterials or the corresponding adhesive. Materials, both elastomeric andrigid, have been used for both the surface of the rotor and the statorsubjected to these conditions. For rigid material applications, aclearance between the rotor and the stator replaces the contact sealbetween the two parts formed in other applications when using anelastomeric seal. The clearance between the rotor and stator is eitherdesigned, or worn into the rotor and/or stator during operation. Such adesign can significantly reduce the efficiency due to the volume of theworking fluid passed between the I.D. of the stator and the O.D. of therotor. Such pump/motor designs are not favored in most applicationsbecause of their poor efficiency.

Progressing cavity pump/motors are disclosed in U.S. Pat. Nos.6,120,267, 6,491,501, 6,695,060, 7,214,042, 7,407,372, 7,553,139, andPublications US 2010/0316518 and US 2010/0322808. Such pumpsconventionally contain an elastomeric layer on the inner surface of thestator for deforming during rotation of the rotor to form a contactseal. U.S. Pat. No. 7,837,451 discloses a rotor with lobes and groovesin the casing for use in pulse detonation combustors (PDC's) and engines(PDE's). Grooves are provided on a tip portion of the lobes andpresumably increase air pressure to the combustion chamber. Pumps andmotors according to the present invention rely upon a working fluid,which conventionally is a mixture of liquids, solids, and often somegas, to generate energy or to transfer fluids.

The disadvantages of the prior art are overcome by the presentinvention, an improved pump/motor is hereinafter disclosed.

SUMMARY OF THE INVENTION

In one embodiment, a progressing cavity pump/motor includes a statorhaving an interior surface and two or more spiraling internal lobes. Therotor has an exterior surface and one or more spiraling external lobes,with the rotor cooperating with the stator to form progressing cavitiesbetween the stator and the rotor during rotation of the rotor. At leastone of the stator interior surface and the rotor exterior surface has aplurality of spaced grooves in its surface, such that fluid flowing to agap between the stator and the rotor is disrupted by the spaced groovesto reduce leakage between the stator and the rotor.

These and further features and advantages of the present invention willbecome apparent from the following detailed description, whereinreference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a stator and a rotor according tothe present invention.

FIG. 2 is a detailed cross-sectional view of a portion of the pump/motorshown in FIG. 1 with grooves formed in the exterior surface of thestator and a gap between the stator and the rotor.

FIG. 3 is a cross-sectional view of a portion of a stator illustratingaxially spaced grooves.

FIG. 4 is an enlarged view of alternative grooves.

FIG. 5 illustrates yet another groove configuration.

FIG. 6 illustrates alternative deeper and narrower grooves than shown inFIG. 5.

FIG. 7 illustrates a stepped grooves within the stator surface.

FIG. 8 illustrates a portion of a stator with sets of spaced grooves.

FIG. 9 illustrates in more detail the grooves shown in FIG. 8.

FIG. 10 illustrates a three-groove set and a series of spaced grooves.

FIG. 1 illustrates spaced grooves on the rotor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The substantially rigid stator interior surface and rotor exteriorsurface in a progressing cavity pump/motor incorporate a clearance orgap between the rotor and the stator surfaces. This clearance allows therotor to turn inside the stator. The clearance is large enough to allowsmall solid particles, sometimes carried in the working fluid, to passthrough without binding the rotor and the stator. Flow resistancethrough the non-contact seal formed by the gap between the rotor and thestator is created by choke flow wherein the fluid particles cannot movearound each other. The present invention significantly increases theeffective flow resistance of this non-contact seal, therebysignificantly decreasing fluid loss between the rotor and the statorwhile there is a nominal gap between the rotor and the stator.

Those skilled in the art appreciate that the seal line between the rotorand the stator is moving in a cyclical manner as the pump/motoroperates. The velocity and direction of flow at any point on the rotoror stator surface is therefore constantly changing in a repeatingpattern. Near surface flow will be substantially parallel to the statoror rotor surface, but, at locations near the seal line, the flow canimpinge at angles approaching perpendicular. This rapid cyclicalvelocity offers a certain amount of resistance when the rotor and statorsurfaces approach each other. This resistance is minimized, however, bythe conventional smooth, contoured surface on both the rotor and thestator surfaces.

The present invention incorporates small and preferably parallel grooveson the surface of either the rotor and/or the stator to create turbulenteddies in the near surface flow. This substantially increasesturbulence, which results in an increase in flow resistance and thus asignificant decrease in fluid leakage. The groove design (shape, depth,spacing between grooves, and orientation) determines the amount of flowresistance achieved. Eddies are created by “tripping” fluid flowingalong the contoured surface as it flows across the groove, or byredirecting fluid that impinges the groove from oblique angles. Asdiscussed hereafter, turbulence generation may be increased with theaddition of steps, walls between closely spaced grooves, and acombination of walls and steps.

Referring now to FIG. 1, the progressing cavity pump/motor includes astator 12 having an internal surface 14 and two or more spiraling lobes16. The rotor 18 includes an exterior surface 20 and one less lobe 22than the stator, thereby forming progressing cavities between the rotorand the stator as the rotor rotates within the stator. A progressingcavity pump/motor as shown in FIG. 1 may thus be used as a pump whichmay be powered by a work string from the surface to pump fluids to thesurface for hydrocarbon recovery, or may be used as a motor which ispowered by hydraulic fluid pumped down to the motor and used to performa mechanical function, such as rotating a shaft which then drives adrill bit. As suggested above, the vast majority of downholemotors/pumps of a progressing cavity type include a metal stator body,an elastomeric layer on the interior surface of the metal stator body,and a metal rotor which rotates and forms a contact seal with theelastomeric layer as the rotor rotates with respect to the stator. Thesame type of motor/pumps are sometimes operated, at a greatly reducedefficiency, with a clearance between the rotor and stator.

The present invention is substantially different in that the primarysealing mechanism is non-contact with grooves specifically designed toincrease motor/pump efficiency. FIG. 2 illustrates a plurality oflocations 26 where the rotor surface approaches the stator surface. Eachlocation is a part of the seal area including at least one groove in theinner surface of the stator and/or in the outer surface of the rotor, asexplained further below. Some fluid will leak between the rotor and thestator. The amount depends on the viscosity and velocity of the workingfluid, the size of the gap, and the number and type of grooves 30. Thegrooves 30 provide a significant resistance to the flow moving towardand through the gap by generating disturbances which convert kineticenergy into heat, thereby significantly reducing the amount of fluidwhich passes through the gap and increasing the efficiency of thepump/motor.

FIG. 3 illustrates the portion of a stator 12 with a series ofrectangular-shaped elongate grooves 30 with sidewalls generallyperpendicular to the groove surface. Those skilled in the art shouldunderstand that the grooves preferably extend through substantially thelength of the stator, and also are preferably aligned with a centerlineof one of the stator lobes. The seal location between the rotor and thestator is constantly changing, but the spaced grooves 30 as shown inFIG. 3 provide a significant disturbance to fluid flow to reduce thefluid loss and increase pump efficiency.

FIG. 4 is an enlargement of a variation of the grooves shown in FIG. 3,and illustrates a generally rectangular groove configuration withslanted sidewalls, so that the entrance to the groove 32 is wider thanthe base of the groove. FIG. 5 illustrates another type of groove formedin the inner surface of the stator, with this groove 34 having agenerally curved or accurate cross-sectional configuration. The groove36 in FIG. 6 is similar to the FIG. 5 groove, although the groove widthis decreased and the groove depth is increased. FIG. 7 illustrates astepped groove design, wherein one portion 37 of the groove 38 has ashallower depth than an adjacent portion 39 of the same groove 38.

FIG. 8 illustrates an alternative portion of a stator 12, and again onlyan axially short portion of the grooves are shown for clarity. Thegrooves in FIG. 8 are provided in sets 40, with a stator interiorsurface 14 spaced between each groove set. FIG. 9 is an enlargement ofone of the groove sets 40 shown in FIG. 8, and illustrates the grooveset comprising an accurate groove 42 followed by a generally rectangulargroove 44.

In other embodiments, each groove set may consist of three or moregrooves, as shown in FIG. 10, wherein each groove set 50 of threegrooves spaced apart by the interior surface 14 of the stator, with thegroove set comprising a stepped groove 52, a generally rectangulargroove 54, and another stepped groove 56.

FIG. 11 illustrates grooves 30 each similar to that shown in FIG. 3formed on a portion of the exterior surface of a rotor 18. The rotorgrooves 30 may follow the contour of the rotor lobes, and may beconfigured according to the alternative groove designs disclosed herein.In some applications, it may be preferable to provide the grooves on therotor rather than the stator, and in other applications the grooves maybe provided on each of the rotor and the stator.

The grooves on the inner surface of the stator are elongate in that eachgroove has a length significantly greater than its width. Continuousgrooves may be formed along substantially the entire length of thestator housing, or a discrete length axially extending groove may beformed, followed by a short interval of no groove, followed by acontinuation discrete length axially extending groove, etc. Each groovemay have one outwardly slanted side wall, and a “straight” side wallwhich is substantially perpendicular to the interior surface of thestator. In another alternative, both the side walls of the groove may betapered outwardly, but at different angles relative to a centerline ofthe groove.

Each axially extending groove which matches or follows the contour of arespective lobe on the stator or the rotor will be a substantiallyuniform spacing from a respective lobe centerline. The spacing betweenelongate grooves is relatively short so that the lands between thegrooves (e.g., the interior surface of stator not having a groove) for apreferred embodiment may occupy from two to ten times the surface areaof the grooves.

The benefits of the invention may be realized because downholeapplication systems use better filtering techniques than in decades pastfor recovering solid particles before the fluid enters the pump/motor.In some applications, for example, water may be used as a working fluidwhen drilling out plugs in a well. Also, some applications utilize ahigher viscosity working fluid than was used a decade ago, andaccordingly this higher viscosity fluid further benefits from the use ofgrooves as disclosed herein to disrupt fluid flow to the gap between therotor and the stator.

The pump/motor can become locked by particles wedged between the rotorand the stator if the particles passing through the pump/motor arelarger than the gap. Decreasing the gap between the rotor and the statorreduces the amount of “lost” fluid which passes through the gap, butincreases the likelihood of solid particles becoming wedged between therotor and the stator. The addition of fluid flow disrupting groovesreduces this lost fluid while maintaining a sufficient gap between therotor and the stator of a progressing cavity pump/motor to minimize oreliminated locking. Costs are incurred to provide such grooves in aprogressing cavity pump/motor compared, for example, to providing aspaced groove surface and gap between a cylindrical shaft with a uniformdiameter and a uniform diameter bore in a housing. Unlike othersituations, the spacing between a groove and the ever changing gaplocation varies as the pump/motor is operated. Moreover, providinggrooves along the contoured surface of a lobe is more complicated,particularly since the grooves effectively need to be provided oversubstantially the entire length of the pump/motor, which may be twentyfeet or more in length. Grooves in the rotor and the stator may beformed using machining techniques which are commonly used to form therespective lobes on the rotor and/or on the stator.

The progressing cavity pump/motor of the present invention includes astator with a substantially rigid interior surface in the form ofspiraling internal lobes, and a rotor with a substantially rigidexternal surface and one or more spiraling external lobes. At thetemperatures and pressures in which the pump/motor is operating, thesesurfaces are substantially rigid. As used herein, “substantially rigid”means a surface of any material with sufficient geometric stability atits operating temperature and pressure such that the flexibility of thesurface does not create or contribute to sealing or to reduced loss ofthe working fluid between the surfaces. This includes pliable or elasticmaterials which “cure”, “set”, or “age” to meet the definition of“substantially rigid” under operating conditions.

The “lands” or spacing between the grooves allow the interior surface ofthe stator to act as a guide to facilitate rotation of the rotor withinthe stator. Accordingly, these surfaces cyclically engage at severallocations along the length of the pump/motor to guide rotation of therotor within the stator. A contact seal is not achieved apart from thesespecific locations. Grooves, at intervals along each of the respectivelobes, are provided on the interior of the stator or on the exterior ofthe rotor to minimize fluid losses through the gap by generatingturbulence and effectively reducing the gap width. Groove depth may varyfrom 0.001 inches to 0.100 inches.

A metal stator and rotor may be formed from steel, since it is asuitable substantially rigid material, although composite materials andsome thermoset materials also have this substantially rigid feature, andalso provide high chemical resistance to various types of downholefluids. The gap between the rotor and the stator may vary from 0.000inches to a point of maximum cavity width. Lost fluid passing throughthis gap is significantly reduced by the use of grooves as disclosedherein.

The addition of grooves in the surface of the stator or rotor reducesthe loss of working fluid passing through the pump/motor, therebyincreasing efficiency. In other applications, the size of debris in theworking fluid mandates a large gap between the rotor and stator, suchthat the efficiency of the pump/motor becomes unattractive. By providingthe grooves as disclosed herein, a sufficiently large gap may bemaintained to pass sizable debris while still resulting in a pump ofreasonable efficiency.

The pump/motor disclosed herein is particularly well-suited for downholeapplications, e.g., in oil and gas drilling and fluid recoveryoperations. The pump/motor has significant benefits in otherapplications, particularly in applications involving high temperatureenvironments and/or fluids deleterious to elastomers.

Although specific embodiments of the invention have been describedherein in some detail, this has been done solely for the purposes ofexplaining the various aspects of the invention, and is not intended tolimit the scope of the invention as defined in the claims which follow.Those skilled in the art will understand that the embodiment shown anddescribed is exemplary, and various other substitutions, alterations andmodifications, including but not limited to those design alternativesspecifically discussed herein, may be made in the practice of theinvention without departing from its scope.

What is claimed is:
 1. A progressing cavity pump/motor, comprising: astator having an interior surface and two or more spiraling internallobes; a rotor having an external surface and one or more spiralingexternal lobes, the rotor cooperating with the stator to formprogressing cavities between the stator and the rotor during rotation ofthe rotor; and at least one of the stator interior surface and the rotorexterior surface having a plurality of spaced grooves in the respectivesurface and spaced substantially along the length of the respectivestator interior surface or rotor exterior surface, such that fluidflowing through a gap between the stator and the rotor is disrupted bythe spaced grooves to reduce fluid leakage between the stator and therotor.
 2. A progressing cavity pump/motor as defined in claim 1, whereineach of the plurality of spaced grooves is substantially parallel to acenterline of the respective spiraling lobe.
 3. A progressing cavitypump/motor as defined in claim 1, wherein at least one of the pluralityof spaced grooves is a stepped groove having a first portion withshallower depth than a second portion.
 4. A progressing cavitypump/motor as defined in claim 1, wherein at least one of the pluralityof spaced grooves has a curvilinear cross-sectional configuration.
 5. Aprogressing cavity pump/motor as defined in claim 1, wherein grooves areprovided in sets of two or more differently configured grooves, with arespective surface spaced between groove sets.
 6. A progressing cavitypump/motor as defined in claim 1, wherein a surface spacing betweengrooves or sets of grooves is from 0.1 to 1.2 inches.
 7. A progressingcavity pump/motor as defined in claim 1, wherein the plurality of spacedgrooves are formed on the interior surface of the stator.
 8. Aprogressing cavity pump/motor as defined in claim 1, wherein each of theplurality of grooves has a groove depth from the respective surface offrom 0.001 inches to 0.100 inches.
 9. A progressing cavity pump/motor,comprising: a stator formed having an interior surface and two or morespiraling internal lobes; a rotor having an external surface and one ormore spiraling external lobes, the rotor cooperating with the stator toform progressing cavities between the stator and the rotor duringrotation of the rotor; and at least one of the stator interior surfaceand the rotor exterior surface having a plurality of spaced grooves inthe respective surface, each of the plurality of spaced grooves beingsubstantially parallel to a centerline of the respective spiraling lobe,such that fluid flowing to a gap between the stator and the rotor isdisrupted by the spaced grooves to reduce fluid leakage between thestator and the rotor.
 10. A progressing cavity pump/motor as defined inclaim 9, wherein at least one of the plurality of spaced grooves is astepped groove having a first portion with shallower depth than a secondportion.
 11. A progressing cavity pump/motor as defined in claim 9,wherein at least one of the plurality of spaced grooves has acurvilinear cross-sectional configuration.
 12. A progressing cavitypump/motor as defined in claim 9, wherein each of the plurality ofgrooves has a groove depth from the respective surface of from 0.001inches to 0.100 inches.
 13. A progressing cavity pump/motor as definedin claim 9, wherein a surface spacing between grooves or sets of groovesis 0.1 to 1.2 inches.
 14. A progressing cavity pump/motor as defined inclaim 9, wherein the plurality of spaced grooves are formed on theinterior surface of the stator.
 15. A progressing cavity pump/motor asdefined in claim 9, wherein the plurality of spaced grooves are formedon the exterior surface of the rotor.
 16. A stator for a progressingcavity pump/motor including a rotor having a substantially rigidexternal surface and one or more spiraling external lobes, the rotorcooperating with the stator to form progressing cavities between thestator and the rotor during rotation of the rotor, the statorcomprising: the stator having a substantially rigid interior surface andtwo or more spiraling internal lobes; and the stator interior surfacehaving a plurality of spaced grooves, such that fluid flowing through agap between the stator and the rotor is disrupted by the spaced groovesto reduce fluid leakage between the stator and the rotor.
 17. A statoras defined in claim 16, wherein each of the plurality of spaced groovesis substantially parallel to a centerline of a stator spiraling lobe.18. A stator as defined in claim 16, wherein at least one of theplurality of spaced grooves is a stepped groove having a first portionwith shallower depth than a second portion.
 19. A stator as defined inclaim 16, wherein each of the plurality of grooves has a groove depthfrom the respective surface of from 0.001 inches to 0.100 inches.
 20. Astator as defined in claim 16, wherein at least one of the plurality ofspaced grooves has a curvilinear cross-sectional configuration.